The present invention relates to the control of marine borers using chlorothalonil (2, 4, 5, 6-tetrachloro-isophthalonitrile).
There are a number of conventional preservatives and techniques for preventing the biodegradation of wood in soil contact. However, most of these materials and techniques prove much less effective in a marine environment. The use of creosote treated wood is well known, and is often reasonably effective against some organisms and in cold water marine environments. In warmer waters where crustacean borers are often quite prevalent creosote treatment has proven far less effective, and against some species almost totally ineffective.
In an article entitled "Marine Wood Biodeterioration and Wood Boring Crustaceans" (Proceedings-Marine Biodegradation GOA pages 167-188; 1986), the author, P. J. Boyle, notes that today creosote is by far the most widely-used preservative in marine environments but that where replacing wood piles is difficult or impossible, reinforced concrete piles are often used in spite of their significantly higher cost. The article also notes that appropriate concentrations of creosote provide good protection against all of the economically important marine wood borers except the Limnoria species, especially Limnoria tripunctata.
The article goes on to note that the only wood preservatives with effectiveness against Linmoria borers are chromated copper arsenate (CCA), ammoniacal copper arsenate (ACA), and tributyl tin oxide (TBTO). Unfortunately, while these heavymetal preservatives provide substantially improved protection against borers, they can also significantly reduce the strength of wood, leaving the piles brittle. In addition, these materials raise significant environmental concerns because of the highly toxic nature of the heavy metals that they contain.
A publication of the United States Department of Agriculture Forest Service, "Comparison of Preservative Treatments in Marine Exposure of Small Wood Panels" by Johnson and Gutzmer, published in Apr. 1990, also discusses the difficulty of treating wood to control Limnoria species. The article details results of testing of a variety of different preservative candidates including oil-type preservatives, waterborne preservatives, dual treatments and chemical modification. Among the waterborne preservatives evaluated were the chromated copper arsenate and other heavy metal arsenates of the type discussed by Boyle. The attempted chemical modifications involved the use of propylene oxide, butylene oxide, butylisocyanate and dimethylformamide. The oil type preservative systems evaluated involved various grades of creosote, either alone or in conjunction with insecticides such as chlorinated hydrocarbons, and the article notes that an organophosphate compound, chlorpyrifos, imparted added resistance to Limnoria.
Limnoria is a tiny but very destructive crustacean that burrows just below the wood's surface. This creature bores not only for protection but also for food, digesting the wood. As wave action and friction wear away the weakened wood, the borer digs deeper for protection as well as for additional food. Collectively, masses of these creatures can narrow the diameter of an underwater pile at a rate of one inch or more per year, and at even higher rates in warm tropical waters, eventually causing the infested pile to take on a characteristic hourglass shape.
The most widely employed method of stopping an attack, once actually started, is to wrap the pile tightly with a plastic (about 30 mil in thickness) sheeting from well below the mud line to above the high water line. This will kill the existing borers by eliminating the oxygen supply, while also precluding a subsequent attack. Alternatively, other types of jacketing or chemical barriers have been tried. In every case, these procedures are complex and expensive.
It is one object of the present invention to provide a method of controlling marine borers.
It is another object of the present invention to provide a method of treating wood to prevent degradation by marine borers.
It is yet another object of the present invention to provide a method of preventing and controlling Limnoria infestations.
It is a still further object of the present invention to provide a method of preventing and/or controlling marine borer infestation in which the concentration of environmentally objectionable treatment agents can be substantially reduced.